Gate-Controlled Spin Current Diverter Using 2D Topological Insulator and Normal Metal Junction

Abstract

Two-dimensional topological insulator (2DTI)-normal metal (NM) junction is proposed as a spin diverter. The helical edge state of 2DTI hybridized with the quantum well state of normal metal is well studied in this article. The helical edge state near contacted edge penetrates to NM via spin independent coupling that preserving time reversal symmetry and flows into the NM lead while the isolated edge state flows into 2DTI lead. Energy gap will be opened for one spin thus reducing the spin current for NM channel and the preserving of time reversal symmetry makes the whole spin channels to be complementary. By modulating the Fermi energy for gate control, it is possible to convert the quantum spin hall system into a spin diverter. (Left figure) Schematic of spin current diverter composed of 2DTI-NM junction. Attaching normal metal makes helical electron near it (spin up electron) penetrating to lead2 that preserves the time reversal symmetry and the spin-momentum locking behaviour of isolated 2DTI ref (1,2), while the helical state of isolated edge (spin down electron) remain transport along the isolated edge.